Given the limitations of current treatments for obsessive-compulsive disorder (OCD), identification of alternative therapies is warranted. The primary aim of the present study will be to provide a test of the efficacy of cognitive therapy (CT) for obsessive-compulsive disorder (OCD). As a secondary goal, some of the mechanisms by which that treatment works will be explored. Three questions will be investigated: (a) Does participation in individual CT result in a clinically significant reduction of obsessive-compulsive symptoms?: (b) Do cognitive strategies exert a specific effect on target compulsions or is the impact more generalized?; and (c) Does depth of emotional experiencing facilitate successful sessions and outcome? To examine these questions, a multiple baseline across behaviors design will be used in which six participants with OCD will undergo standardized CT for 18 sessions. Over the course of treatment, participants will complete weekly batteries that measure OCD symptom severity and important cognitive domains (e.g., responsibility, perfectionism). They will also complete daily diaries of target symptoms including avoidance as well as time spent on and distress, related to specified obsessions and compulsions. Session videotapes will be coded for degree of within-session depth of experiencing. Analyses will include hierarchical linear modeling and exploration of graphical trends to address the objectives stated above.